1. Field of the Invention
The present invention relates to a method of forming a fuse in a semiconductor device and a semiconductor device which includes a fuse. In particular, the present invention relates to a method of forming a fuse in a semiconductor device which can prevent over-etching during a process of forming a fuse and can provide a good quality electrical characteristic.
2. Description of the Prior Art
In the process of forming more than two multi-layered metal conductors, such as address or data lines in SRAM memory cells, when a defect occurs in one or more bits of a SRAM cell, a repair process is performed which replaces the defective cells with excess or redundant cells. To accomplish this, the lines, such as address and data lines, of major or primary cells are connected to their counterparts in redundant cells by conductors which include fuses. The fuses can be selectively activated such as by laser to interrupt the continuity of the conductor and therefore disconnect the redundant cell from the primary cell. The repair process involves activating the fuses in the lines which connect redundant cells to functional primary cells. As a result of the repair process, only the fuse metal lines which connect the lines of the primary cells in which defects occurred to the lines of the redundant cells are left intact, and the remaining fuse lines are removed. Thus, the repair process prevents a malfunctional, thereby recovering overall performance of the chip.
In FIG. 1, there is shown a plan view of metal conductors in a semiconductor device with which a conventional multi-layered conductor structure is provided, and in FIG. 2A, there is shown a sectional view taken along the line A-A' in FIG. 1. The plan view of FIG. 1 shows a pattern of the metal conductors 30, typically made of aluminum, in which after the conductors 30 are formed, a fuse metal pattern 40 is formed by etching a barrier metal layer 25, typically made of TiN, which was deposited before the metal layer from which the conductors 30 are formed. After the etching, the portion 40 of the metal between the conductors 30 forms a fuse 40 which can be activated by laser cutting to break the connection between the conductors 30. The structure of FIG. 2A includes an insulating layer 1 on a semiconductor device on which are formed underlying metal conductor layers 10, an interlayer insulating film 15, via metal layers 20 connecting the underlying conductor layer 10 and conductors 30, and insulating film 35 which can be made of an oxide.
FIGS. 2B-2F illustrate the process of forming the device shown in FIGS. 1 and 2A. FIG. 2B illustrates the TiN barrier layer 25 formed on top of the interlayer insulating film 15. In the next step, as shown in FIG. 2C, the layer 30 from which the top conductors 30 will eventually be formed is deposited on top of the barrier layer 25. In one embodiment, the conductor layer 30 is formed of aluminum. The barrier layer 25 and conductor layer 30 are formed over via holes filled with via contact metal 20 such that the upper conductor layer 30 is in electrical contact with the lower conductor layer 10.
In the next step, as shown in FIG. 2C, a photoresist mask 31 is formed over the conductor layer 30. Next, a dry etching process is performed to form the conductor pattern 30. The dry etching removes both the aluminum layer 30 and the underlying TiN barrier layer 25 in selected regions. For example, as shown in FIG. 2D, the dry etching process leaves the pattern of conductors 30 and barrier layer 25 on the insulating layer 15 separated by gaps or channels 41.
As illustrated in FIG. 2D, the gaps 41 separate portions 30B of the conductor layer 30 from the portion 30A of the conductor. Next, as shown in FIG. 2E, an oxide layer 35 is formed over the conductor layer 30. Next, a second photoresist mask 37 is formed over the oxide layer 35 such that an opening in the mask 39 provides access to the conductor 30A. The opening 39 is positioned over the barrier layer 25 to define the position of the fuse portion 40 of the barrier layer 25.
Next, both a dry and highly selective wet etching process are performed to remove the oxide 35 and the conductive aluminum layer 30A in the opening 39. The dry etching step is used to remove the oxide layer 35 and much of the aluminum 30. Because the dry etching process tends to be difficult to control and therefore can easily overetch, the dry etch is stopped before it reaches the bottom of the aluminum conductor 30A. Then, a highly selective wet etching process, which removes only aluminum and leaves TiN intact, is used to remove the remainder of the aluminum in the conductor 30A. The selective wet etching is used to prevent any over-etching into the barrier layer 25 since any such over-etching would damage the fuse portion 40 and render it ineffective for use as a fuse. As shown in FIG. 2F, the remaining conductors arc connected by the remaining fuse portion 40 of the barrier layer 25.
Hence, the process of forming devices illustrated in FIGS. 1 and 2A-2F can be time consuming, inefficient, and, therefore, expensive due to the need for special etching steps to protect the fuse material. Also, because the resulting device is located at the top layer, both the fuse layer 40 and the sides of the conductors 30 are vulnerable to external damages and undesirable contact with foreign matter.